The present invention concerns a timepiece provided with a calendar mechanism activated each day by the timepiece movement and capable of displaying the date in accordance with the traditional Chinese calendar.
The Chinese calendar is still used nowadays to set the date of various festivities and for Chinese astrology. It is of the luni-solar type, in that it is based on lunar months which each begin on the day of the new moon, whereas the length of the Chinese years varies so as to be as close as possible to the tropical year.
The Chinese year starts on the second new moon that follows the winter solstice, with rare exceptions. Given that the length of the lunations is not constant and that its mean value (29.53088 days) is not equal to an integer number of days, the Chinese calendar includes long months of 30 days and short months of 29 days. No cycle of long and short months has been able to be defined.
Moreover, in order for the mean length of the Chinese years to coincide with that of a tropical year, normal years of twelve months and bissextile years of thirteen months, in which the extra month, called the bissextile month, is inserted in a position—- i.e. a row-which varies from one bissextile year to another as a function of astronomic data. This month takes the number of the preceding month, such that the last month of a year always takes the number 12. One inconvenient fact for a mechanical Chinese calendar display is that a position cycle of the bissextile month in the year has not been able to be defined.
Normal years can comprise 353, 354 or 355 days, whereas bissextile years can comprise 383, 384 or 385 days. Normal and bissextile years follow each other practically in a cycle of nineteen years, which corresponds to the Méton cycle of the Greek calendar and includes almost integer numbers of days, lunations and Chinese years, with twelve normal years and seven bissextile years. However, this cycle is not precise long term.
For further data as to the Chinese calendar, the reader can refer to the work of Nachum DERSHOWITZ and Edward M. REINGOLD, Calendrical Calculations, Cambridge University Press, 1997, and to the publications of Helmer ASLAKSEN: The Mathematics of the Chinese Calendar, 13 May 2004, and LeapMonths.nb, Mathematics package, 1999, available on the website.
Because of the peculiarities of the Chinese calendar summarized above, it is not currently possible to make a display mechanism for the dates of this calendar that can be driven by a timepiece movement and that can operate precisely long term without manual intervention, as can the known perpetual Julien or Gregorian date mechanisms, for example in accordance with CH Patent No. 660 440, or as provided by EP Patent No. 606 576 for a Muslim calendar display.